Method and apparatus for fusing refractory materials



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METHOD AND APPARATUS FDR FUSING REFRACTORY MATERIALS Filed May 8, 1944 7 Sheets-Sheet 1 \ba- FEED D UBT COLL E CTOR and.

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METHOD AND APPARATUS FOR FUSING REFRACTORY MATERIALS Filed May 8, 1944 7 Sheets-Sheet 2 CAR. 'raANJ'Fem MECHANIJ'M lLlGTIOOl CONTROL. MIGHANIJ'M 52 CAR- TEKNJ'FER.

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METHOD AND APPARATUS FOR FUSING REFRACTORY MATERIALS Filed May 8, 1944 7 Sheets-Sheet 4 Rqqmond 2. Qldgudy Sept. 2, 1947. R. R. RIDGWAY 2, 3

IB'IHOD AND APPARATUS FOR FUSING REFRACTORY IATERIALS Filed lay 8, 1944 7 Sheets-Sheet 5 I 129ml film 135a,

Reva-225151.: DC Mo'ron. OPERATED ELECTRODE ELEVATOR. MECHANESM REVERSIBLE DC. M0102 OPERATED ELECTRODE ELEVATOR. MECHANISM REVERSIBLE D.C.

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p 1947. R. R. RIDGWAY 2,426,643

IEI'HOD AND APPARATUS FOR FUSIHG REFRACTORY IATHRIALS Filed lay 8, 1944 '7 Sheets-Sheet 6 :4 lzNoou 1PM. 2.9M- ;RM. 42M.

FIG. 15 3mm Raymond R. B ldguqy Sept. 2, 1947. R. R. RIDGWAY 3 IETHOD AND APPARATUS FOR FUSI NG REFRACTORY IATERIALS Filed lay 8 1944 7 Sheets-Sheet '7 Raymond 3. kids we.

Patented Sept. 2, 1947 METHOD AND APPARATUS FOR FUSING REFRACTORY MATERIALS Raymond R. Ridgway, Niagara Falls, N. Y., as-

signor to Norton Company, Worcester, Mass, a corporation of Massachusetts Application May 8, 1944, Serial No. 534,653

29 Claims.

This invention relates to a method and apparatus for the continuous production of fused materials of high melting point, of which fused alumina is a good and preferred illustration; alumina (A1203) having a melting point on the order of 2,000 C.

One of the objects of this invention is to provide a practical and dependable method and apparatus for fusing, and then casting for solidification, refractory oxide materials of high melting or fusing point, with such arrangement and sequences of steps in the method and such controls in the operation of the apparatus that substantial continuity of processing of the oxide may be achieved, interrupted only by circumstances, such as th need for repair or replacement of various parts. Another object of this invention is to provide, in a method and apparatus of the abovementioned character, for the dependable and efficient production, for the metallic furnace shell, of a lining capable of withstanding the effects of the high-fusing-point fused material contained therein and of dependably protecting the shell, and for the subsequent maintenance and control of the lining during long-continued operation and throughout such variations or variables as may accompany, or may be made to accompany, the otherwise continuous processing, includin such factors as variability in quantity of the charge or melt, rate and character of supply of unfused or raw material to the furnace, energ or power input to the charge, etc., etc. Another object is to provide a practical and dependable method for producing, and maintaining in proper and safe operating condition, a lining in such a metal furnace shell of the same material as the product undergoing fusing, and to provide steps of procedure and of control to so maintain the lining during and throughout such variable factors as quantity of the melt in the furnace, rate or character of withdrawal of fused material, rate or character of supply of unfused material to the furnace, etc., etc.

Another object is to provide a practical method and apparatus for achieving the reliable and consistent casting or pourin of the high-fusingpoint refractory oxide at suitable degree of superheat where it is desired to give the final product, such as the cast and ultimately solidified alumina, certain desired characteristics, particularly as to character and extent of pore structure, character of crystalline structure, etc., etc. Another object is to provide a simple and practical method and apparatus for achieving simple and reliable access, particularly throughout and during long continuity of operation, to regions of the melt that are of the desired superheat for withdrawal of superheated molten material therefrom for pouring or casting. Another object is to provide a method for producing and maintaining a lining of the above-mentioned character for proper functioning thereof throughout such a variable as change in relation between the electrodes by which the charge or melt is heated and the furnace and. lining containing the charge.

Another object is to provide a method and apparatus for fusing high-fusing-point material, such as alumina, that will be capable of being carried on or operated in practice under conditions of substantial continuity of feed or supply to the furnace charge or melt of unfused or raw material and of withdrawal of fused material from the charge or melt, for casting or solidification and crystallization, without detrimentally affecting Or disturbing the thermal conditions of the melt from which the fused material is withdrawn and without contaminating the fused material being withdrawn by admixture therewith of unfused or partially fused material. Another object is to provide a method of controlling and operating an electrical furnace for fusing high-fusing-point material and a series of molds or receptacles for receiving fused material from the furnace, in such a manner as to achieve eiiicient, lower cost, and substantial continuity of largequantit production with repeated and successive employment of the molds or receptables. Another object is to provide a method for dependably and reliably correlating, for substantially continuous large-quantity production of crystallized or so lidified fused material, like alumina, such factors as rate of feed of unfused or raw material to the electric furnace, rate and character of withdrawal therefrom into molds or receptacles, power input, cooling or solidification of the withdrawn material, and the like.

Another object is in general to provide an im proved method and apparatus for the safe, dependable, continuous quantity-production of fussed high-fusing-point refractor oxides, such as alumina, having the desired ultimate qualities and characteristics, and capable of being economically carried on commercially. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts and in the several steps and relation and order of each of the same to one or more of the others, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings in which are shown one or more illustrative or preferred embodiments of the mechanical features of this invention,

Figure 1 is a side elevation, partly diagran matic and partly schematic, of a furnace installation;

Figure 2 is a plan view of a furnace installation and of a preferred and illustrative coacting material-handling system, certain parts being shown in horizontal section or omitted and other parts being shown diagrammatically;

Figure 3 is a front elevation, as seen from the right in Figures 1 and 2, of only the furnace and electrode structure, showing also certain features of the mounting of the furnace;

Figure 4 is a vertical sectional View, on a larger scale, of the furnace structure as seen along the line 4-4 of Figure 2, certain parts being shown in elevation and certain other parts being omitted;

Figure 5 is a vertical sectional View, on a larger scale, of the furnace structure as seen along the line 5-5 of Figure 2, certain parts being shown in elevation and certain other parts bein omitted;

Figure 6 is a horizontal sectional view as seen along the line li-6 of Figure l, certain parts being omitted or indicated diagrammatically;

Figur '7 is a detached or fragmentary vertical sectional view, on an enlarged scale, showing certain relationships between the furnace lining and the pouring spout as seen along the line 4-4 of Figure 2;

Figure 8 is an elevation on a larger scale as seen along the line 83 of Figure 1, showing certain structural relationships between the electrodes and the furnace hood structure;

Figure 9 is a vertical transverse sectional view, on an enlarged scale, as seen along the line 9-4) of Figure 8, showing in detail certain of the struc tural features inter-relating the electrodes and the hood structure;

Figure 10 is a detached or fragmentary side elevation showing certain features of construction of the sides of the hood;

Figure 11 is a vertical sectional View as seen along the line i l-l l of Figure 10;

Figure 12 is a diagrammatic representation of circuit and control arrangements for the energization and control of the electrical features of the furnace;

Figure 13 shows, by way of graphs, a number of operating characteristics, over a 4-hour period of continuous operation;

Figure i l is a horizontal sectional view of the furnace shell to show in elevation, with certain parts being broken away, one stage in the construction of a modified form of bottom lining, and

Figure is a vertical sectional View as it would be seen along the line ll of Figure 2, the view bein partly broken away and partly shown in elevation, showing the completed bottom and side lining for the furnace shell, and being therefore a transverse vertical section along the line |5-l5 of Figure 14: in the final stage of completion of the bottom and side lining.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Referring to Figures 1, 2 and 3, the furnace comprises a shell generally indicated by the reference character If], preferabl also a top closure or hood generally indicated by the reference chain acter l I, and an electrode assembly, mounting,

and control, all generally indicated by the reference character I2, with the electrodes, which are three in number where 3-phase electrical energy is to be employed and which are indicated by the reference characters l3, l4 and I5, projecting downwardly into the interior of the shell l0 which, in turn, is preferably constructed and mounted to be tiltable and to have preferably certain thermal relationships to the electrodes and to certain other parts, all as later described. It is within the furnace shell 0 that continuous fusion of high-fusing-point material, such as alumina, is to be effected in certain later-described relationships to preferably continuous feed of unfused material thereto and to withdrawal of fused material therefrom.

The shell i0 is preferably made of suitably heavy sheet steel and, while provided internally, at least throughout certain portions thereof, with a suitable refractory lining as later described, it nevertheless has to be protected against excessive temperature rise therein, particularly where the material to be fused is alumina, which will hereinafter be used illustrativel and which has a temperature of fusion or melting point on the order of 2,000 C. Such protection I provide by flowing continuously over its external surfaces a good heat-abstracting-medium, such as Water, and to that end, as well as to achieve certain other coactions and advantages later described, I prefer to give the shell ID a generall frusto-conical shape as by correspondingly forming or building up its side shell l6 and by giving its bottom I! a shape substantially like a segment of a sphere preferably of a radius having a preferred relationship, later described, to certain other thermal relationships within the furnace ll). With such shape, water may be continuously sprayed or flowed onto the exterior surfaces of the furnace shell ll], with cumulative protective action as is later described.

Sheet steel comparable to boiler plate may be employed in building up the shell l0 and joints or junctions are preferably butt-welded to give relative smoothness of surface, both exteriorly and interiorly and, while the spherical segment making up the bottom shell I0 is preferably of a single piece, it may be built up of sector-shaped segments, three of which, H ll and ll are visible in Figure 1, welded together and peripherally welded to the bottom periphery of the side shell [6.

In order to achieve relationships and coactions later described, one portion of the side wall, indicated at NS in Figures 1, 2 and 3, While still sloping downwardly and outwardly as do the remaining curved side wall portions lfi substantially straightens out in horizontal cross-section (see Figure 2), forming 3, preferably plane wall portion that merges tangentially into the curvature of the curved portions l6 which can be and preferably are of substantially the same radius; this fiattene'd-out wall portion Hi I shall hereinafter call the front wall of the furnace shell H). In effect, therefore, the preferred form of the side shell I6 is, geometrically speaking, circular throughout substantially 270 (the curved Wall portion HF) and substantially straight along a chord which subtends substantially thus to form the front wall Ili In Figure 2, the center or vertical axis of curvature of the curved wall portion I6 is indicated by the point P and where three electrodes l3--l4| 5 of graphite, or the like, are employed, they are preferably arranged vertically With their vertical axes respectively at the apexes of an equi-lateral triangle having one of its sides parallel to the straight front wall Mi and with the apexes of the triangle and hence the centers of the electrodes equi-distant from the nearest points in the curved wall portion l6 of the side shell l6; that is to say, in the preferred arrange" ment, the distances B, indicated in Figure 2, are equal or substantially so. The electrode mounting and assembly [2 is therefore, in the preferred form, constructed to support and position the electrodes relative to the furnace shell 10 to achieve the relationships just described and also others later herein set forth.

The electrode mounting I2 may be of any suitable or desired detailed construction and, illustratively and preferably, I provide individual supports, preferably and individually movable and controllable, for the respective electrodes. Thus, where the latter are three in number, I ma provide three vertically movable masts i9, and 2| provided with suitable horizontal cantilever arms or jibs 22, 23 and 24, respectively, each supporting an electrode in its outer end by any suitable insulatingly mounted and preferably watercooled clamp, generally indicated by the reference character 25; each clamp is preferably also provided with any suitable means, such as a hand-wheel-and-screw, generally indicated at 26, for releasing or tightening the clamp on the electrode, so that each may be initially set, or subsequently re-set downwardly as it is consumed during operation, in order thereby to achieve the same lengths of the three electrodes projecting downwardly from the jibs 22, 23 and 24. With the latter set in substantially the same horizontal plane, the lower ends of the electrodes are likewise in substantially the same plane transverse of the axis P of the furnace shell ID.

The three masts l9-20 and 2| are suitably supported and controlled for up and down movement, for either manual, or motor-operated, or automatic actuation thereof, not only for purposes of initially mounting the electrodes in the jibs or of subsequently setting them downwardly with respect to their clamps, but also for purposes of setting them, during operation of the furnace, properly with respect to the charge and for maintaining them in appropriate relationship to the charge during variations in quantity of the latter or changes in condition that might take place during the operation of the furnace; thus the three masts I9, 20 and 2| may be polygonal in cross-section (Figure 2) and extend downwardly into suitable guideways 2'! provided in a casing-like standard 28 which is preferably constructed and mounted separately from the furnace structure I0l| and which can contain appropriate apparatus and mechanisms of known form, such as cables, pulleys, winches, motor drives and hand-wheel drives therefor for effecting movement and control in up and down direction of the masts in the manner above described; such mechanism may take any known form and hence is not shown and of this mechanism only three hand-wheels 29, 30 and 3! are shown in Figures 1 and 2, the remainder of such mechanism being diagrammatically indicated at 32.

Suitable means, also of known form, are provided to lead electrical energy to the electrodes; thus each mast may carry, in suitable insulating supports, a heavy water-cooled conductor 34 connected at its one end electrically to the clamp that holds the electrode and p o ed with means at its other end for making electrical connection 6 y by way of heavy flexible conductors 35 to the power supply circuit, the flexible conductors 35 permitting freedom of up and down movement of the electrode masts while maintaining the electrical connection thereto.

At 36 in Figure l is shown the floor line of the installation and I provide a pit or sump 31 with respect to which the mast supporting standard 28 may be mounted in overhanging relation so as to permit the masts I9, 20 and 2|, if necessary, to descend and project downwardly below the base of the standard 28 where, as is preferred, substantial downward movement of the electrodes and jibs is desirable. The pit 3T preferably extends toward the front of the furnace structure, that is, to the right in Figure 1, illustratively to a point materially short of the vertical axis P of the furnace shell i 0; into the sump 3'1 is to be drained the water that runs off of the exterior surfaces of the furnace shell l0 and from the sump 3! the Water is continuously removed as by a pump 38 of any suitable construction and drive, and preferably the drain-off, as

by the pipe 39, from the sump 3'1 takes place by gravity so that drainage is achieved without risking a failure in the drive of the pump,

The furnace shell it is preferably constructed and mounted so as to normally rest in upright or vertical position, that is, with its axis P vertical, and to be tilted at will in the direction of the above-mentioned flattened-out front wall I6 in which i mounted, preferably in the manner later described, a refractory pouring spout 40 with a removable and preferably refractory plug or closure M, both being preferably made of graphite, so as to effect pouring of liquified contents from the furnace.

Accordingly and illustratively, I provide a suitable number, illustratively two, spaced arcuate rockers 42 and it (Figures 1, 2 and 3) secured to the bottom shell ll preferably in a manner to strengthen the latter and to provide for good distributed support of the load represented by the furnace structure and its contents. Thus each rocker may comprise parallel spaced steel plate elements i l (Figure 3) shaped to fit the curvatures of the bottom shell H to which they are welded in spaced relation, the pair of plates 44-44 of each rocker being bridged by an arcuate plate 55 welded thereto and provided on its downward face with spaced teeth 46 (Figure 1).

The two spaced rockers 12 and 43 rest, respectively, upon two similarly spaced truss-like supports ll and 58, respectively, which may also be built up out of sections welded together, each having an upper supporting plate 59 preferably upwardly convex and provided with holes 50 spaced appropriately to receive the teeth 46 of the furnace shell supporting rockers so as to prevent displacement of the furnace structure during rocking or tilting movement, the truss-like guideways ll and 38 having suitable base plates 5! for resting flatwise against a suitable foundation and for securing them thereto, preferably in position to overhang the sump 31 (Figure 1), the overhanging portions being supported, if

desired, by cross-beams 52 extending across the sump 3?.

Throughout a substantial area greater than the lateral expanse of the furnace structure, excepting for the foundation portion underlying the supporting guideways ll-48, the foundation or flooring is shaped in the form of a shallow pit or basin 53 that slopes downwardly toward and into the pit 3i so that water running off the furnace shell ID that does not drip directly into the pit 31 is caught in the shallow basin pit 53, the slope of which insures quick run-off into the pit 31.

Suitable means are provided for effecting tilting of the furnace structure out of and back into its normal vertical position. Preferably, the shape or curvature of the top plates 49 of the fixed guideways 41 and 4B is such, in relation to the curvature of the furnace shell rockers 42-43, that, for any position of the furnace shell out of its vertical position and within the desired range of tilting, the center of mass oi. the furnace structure and its contents remains always on that side of the vertical plane through the lines of contact of the rockers with the guideways as to return the furnace structure always to its normal vertical position; to tilt it out of its vertical position, that is, clockwise a viewed in Figure 1, I preferably employ any suitable reversible driving mechanism, that is, a mechanism so constructed that it may be actuated in tilting direction by the source of motive power employed and does not resist being actuated or driven in reverse direction when the motive force is the force exerted by the mass of the furnace structure operating through a lever arm that is measured by the above-mentioned spacing of the center of mass from the vertical plane through the lines of contact of the rocker supports with the guideways. With such a mechanism, the application of the source of motive power achieves tilting in clockwise direction in Figure l as may be desired for pouring from the spout 40 and achieves restoration of the furnace structure to normal vertical position for cessation or halting of pouringwhen the source of motive power is I released or removed at will or even when failure of that source of motive power takes place. Thus shut-off of pour of the high temperature fused and liquid material, as by tilting the furnace structure back to normal, thus to permit the in-- sertion of the closure plug 4| in the spout 40 or to bring the discharge opening in the spout 40 above the level of the liquid material within the furnace, may be effected with complete safety and control even if failure of the source of motive power for tilting the furnace takes place.

A suitable and illustrative form of such mechanism may comprise a fluidpressure-operated mechanism, preferably hydraulic, and may include a cylinder 55, pivotally mounted by trunnions 56 (Figures 1 and 3) supported in suitable bearing in spaced plates 51 and 58 secured as by welding to the cross-beams 5252, and having therein a piston whose connecting rod 59 is pivotally connected by a suitable bracket struc ture 6!] preferably bridged across and secured as by welding to the rocker supports 42--43. To the lower end of the cylinder 55 is connected a flexible conduit 61 leading to a suitable source, diagrammatically indicated at 62, of liquid, such as oil under pressure. A suitable valve, diagrammatically indicated at 63, is constructed and arranged so that when set in one position, liquid under pressure enters the cylinder 55 to start tilting the furnace structure, when set in the next position it shuts off the liquid under pressure and prevents escape thereof from the cylinder 55 and thu effects holding of the furnace in tilted position against the action of its own Weight in tending to return it so that thereby the furnace may be held in tilted position for as long as is desired, but when the valve 63 is set in its next position, it connects the conduit Bl to a by-pass or return conduit 64 which leads to the low pressure or sump side of the fluidpressure source 62, thus permitting escape of liquid from the cylinder 55 and permitting the weight effect of the furnace structure to tilt the latter back to normal vertical position, the latter action forcing the piston in the cylinder 55 in retrograde direction to eject the liquid by way of the conduits BI and 64, and thus readying the hydraulic mechanism 55 for a subsequent tilting actuation of the furnace structure under the control of the valve 63.

Failure of the drive of the pump embodied in the fluid-pressure mechanism 52 will thus be seen not to interfere with the return tilt of the furnace for all that need be done is properly to set the valve 63 to its third above-described position.

By means of the valve 63 the extent of tilt may be controlled, as will now be clear. Thus the valve may be actuated to give a certain desired degree of tilt to effect commencement of pouring, and as pour continues and change in head of the high temperature liquid material in the furnace may require change or adjustment in the tilt, appropriate manipulation and setting of the valve 63 readily achieves the desired tilt or change in tilt.

Within the furnace shell 10, I provide a suitable lining of suitable refractory material; according to certain features of my invention and with certain control and eoactions later described, this lining need not be throughout the entire interior of the furnace shell l0 and I am enabled to leave the upper inner wall portions of the latter free from a lining, thu simplifying construction and maintenance. Where the material to be fused is alumina or the like, I provide a lining, preferably of the same material as the material to be fused, namely, in the illustration, alumina, and preferably I employ pure previously-fused alumina, utilizing alumina that has been previously fused and hence shrunk so as to gain the advantages of maximum density alumina for constructing the lining.

Previously-fused alumina is crushed into lumps which range in size from about 3" to sizes as small as grit size after ClllShil'lg it is screened and thus segregated into graded sizes. The resultant lumps are fitted together and superimposed upon one another and the interstices therebetween filled in with smaller sizes, including also the smaller and smallest grit sizes, and in this way a relatively massive lining is manually built up to cover the bottom ll (see Figures 4 and 5) to a depth of about 30", with the surface thereof substantially flat or even concave to substantially follow the contour of the bottom IT, as indicated by the broken line 65, and if desired it may also be built up upwardly about and against the inside faces of the wall portions lb and it of the side shell i6, as indicated by the broken line 66, whereby it is of substantial concavity. If built up to have concavity, it is preferable to maintain substantial concentricity with the vertical axis P of the furnace shell Hi, and lining preferably tapering off against the side wall I6 and [6 the upwardly tapering portion against the front wall it being thinner than the corresponding portions tapering upwardly against the curved side portions Hi because of the geometric relationship of these walls as above described and as appears also from Figure 6. Also, it is preferred to first lay against the inside of the concave bottom shell 11 a bed or layer of granular alumina within which to seat or bed the lowermost layer of the lumps as the lining structure is thus manually built up.

The thus built-up preliminary lining structure is now ready to be converted for later functioning and that I achieve by subjecting it to controlled fusion under the action of the above-described electrodes but since, in so treating it, it is desirable to employ the water-cooling that is to function on the external surface of the furnace shell during subsequent operations of the furnace anyway, the means for achieving such watercooling may at this point be briefly described. Preferably, such means comprises an upper pipe or conduit 69 (Figure 1) that surrounds the upper external portion of the side shell I6, being suitably mounted by suitable brackets and having holes in it to discharge water inwardly and downwardly against the downwardly and outwardly sloping external surface of the side shell 16, thus covering the latter with a downwardly moving film or sheet of water. Partway down and just above the spout 40 is another pipe similarly constructed and mounted and through numerous holes discharging additional water against the external face of the side shell, thus insuring adequate heat-abstracting capacity and also to compensate for loss of water due to evaporation. Extending parallel to the rocker supports 42 and 43 and also in between the plates 44--44 of the latter is a series of pipes H (see also Figure 3) supported in any suitable way by suitable brackets against, or suitably spaced from, the curved bottom shell l'! to the curvatures of which the pipes substantially conform. These pipes have upwardly and outwardly directed holes to spray continuously streams of water against the underface of the bottom shell l0. These pipes as well as pipes 69 and 10 above mentioned are connected through suitable connections, including a flexible conduit (not shown) to a suitable source of water under pressure so that they may discharge water against the entire external surface of the furnace shell [0, even though the latter be tilted. At the front of the furnace shell l0 and spaced away from the plane front wall [6 is suitably supported a shield plate 13 of metal to prevent water that runs along the spout construction from becoming commingled with material being discharged during tilting of the furnace. The shield or guard plate 13 is welded to a metal sleeve 12 that is welded into an opening in the front wall I6 (Figure 4) and within which is removably supported, as later described, the graphite discharge spout 40 above mentioned.

With the built-up and pieced-together bottom and lining structure now in place as above described, and with the cooling water applied, graphite resistor elements in the form of bars or rods are now laid upon the inserted bottom structure to form resistance paths between the lower ends of the electrodes l3, l4 and I5 which are brought down to engage them and also to substantially contact the built-up bottom structure; the resistors thus become effective, when the electric circuits to the electrodes are closed, to start arcing between adjacent electrodes, thus commencin the heating of the pieced-together alumina structure which begins to fuse in its uppermost layer regions and thus becomes conductive, permitting the removal of the graphite resistor elements. During this preliminary heating-up stage, it is desirable to pour on top of the pieced-together structure a quantity of fine grit or pulverized material of the same character, such as pure fused alumina, which under the heat of the arcs becomes fused and liquid and thus facilitates commencing the operation of treatment of the inserted pieced-together bottom structure for ultimate permanent use; the melt of this powdered material will thus be seen also to facilitate starting the fusion or melting of the uppermost layer-like portions or strata of the lump-form of lining, and a considerable charge of such fine grit or pulverized material may be added for these and other purposes about to be described.

In either case and with the fusing started, fusion is continued, but at a controlled rate and at a rate of power input to the electrodes which, in the illustrative size and capacity of furnace here described, is less than the normal or usual rate for operation upon an average ultimate furnace charge of raw or unfused material. Thereby the inserted lump form and pieced-together structure is slowly and progressively brought to fusion, the progression of fusion throughout the mass proceeding downwardl toward the bottom shell ll but being halted at a point short of reaching the bottom shell ll, thus to leave a layer or strata of unfused material of suitable thickness immediately adjacent the bottom shell H, as is indicated at 68. In the course of this fusion, the lumps and pieces lose their identity and become molten excepting for the outermost layer or strata just mentioned, some of the lumps of which, particularly the innermost lumps, are partially fused or are in effect sintered together by the union of only fused superficial layer portions of the lumps themselves. As this fusion progresses downwardly and outwardly, it is aided by liquid or molten material, includin the powdered material with which the furnace is charged as above mentioned, to an appropriate extent, at the commencement of the operation, for the liquid material tends to progress downwardly in whatever spaces or interstices are available between lumps to commence the fusion of the latter. The control of progression of fusion so as to prevent it from reaching the metal shell is preferably effected by manual control of the vertical positions of the electrodes and manual control of the power input to the latter, in order thereby to prevent fused or liquid and hence conductive alumina from being formed or brought into being in direct contact with the metal of the shell, for such contact would bring about arc-over and puncture of the metal of the shell.

The lower ends of the electrodes, even though the latter may be adjusted up or down during this processing, are of course maintained in substantially the same plane transverse to the vertical axis P of the furnace shell Ill and the bottom shell I? is preferably concave and like a segment of a spherical surface to define a line taken in any vertical section, of which Figures i and 5 are illustrative, that is substantially parallel to or coincident with isothermal lines spaced downwardly from the plane of the ends of the electrodes, Or it might be said that, extending downwardly from the somewhat circular (as viewed in horizontal section as in Figure 6) region of maximum temperature encompassing the electrode ends and extending into the conductive fused or liquified material, there are upwardly concave geometrically somewhat similar isothermal surfaces or planes of progressively lessening temperature as the bottom shell I1 is approached,

ill.

and it is to one of these isothermal. planes, of a temperature materially below the fusion point of the alumina, that the bottom shell If more or less conforms in shape. This may be determined empirically and with a bottom shell ll of maximum diameter of 11 feet where it joins the bottom of the frusto-conical side shell I6, the curvature of the spherical segment making up the bottomshell H can have a radius of 11 feet and this I have found gives appropriate or close enough coincidence with the desired isothermal surface or plane, for an ultimate bottom lining thickness of 30" of alumina, to protect the metal of the bottom shell during subsequent continuous operation of the furnace for fusing alumina, with controls such as I later describe.

But during the fusing treatment of the inserted built-up lump form of bottom lining, this preferred concavity of the bottom shell ll greatly facilitates the completion of the formation of the bottom for, as the earlier above-mentioned fusion thereof progresses downwardly, the fusion front advances along upwardly concave surfaces or planes geometrically generally similar to the above-mentioned isothermal surfaces or planes and hence there is a substantially uniform ap proach toward the metal of the bottom shell ll of the downwardly advancing fusion of the alumina that is to form the bottom lining, and thus risk of arc-over to and puncture of the bottom shell is greatly minimized, and testing of the downward progress of fusion, as later described, greatly facilitated and simplified.

Thereby also, halting of the downward progress of fusion, as above mentioned, brings about substantial uniformity of thickness of the unfused or sintered-together layer 68 next to the bottom shell ll itself.

The rate and extent at which fusion progresses downwardly toward the bottom shell H is, during the above process, tested periodically by means of a metal probe bar, which is put down into the furnace shell H] (see Figures 4 and 5) through the upper end and thrust downwardly toward the bottom shell ll; the extent to which it enters the furnace shell [0 in downward direction, knowing the initial depth to which the bottom lining was initially built up in lump form (30" illustratively), permits the determination of the depth to which the lumps and particles of the 30 lining have become liquid, for the end of the probe is stopped by those lumps or portions that are still in unfused condition. If the progression of fusion is non-uniform, and that may be detected by noting, when probing, material variations in depth of liquid material, it means that heat energy is being put into the material at too great a rate, possibly in a manner to distort or materially change the shape of the concave isothermal planes, and that there is risk of a more rapid advance toward the metal bottom shell at one or more points than at others. If the rate of progression of fusion is too great, the risk might be run of a cumulative action which might prematurely bring the fusion front right up to the metal of the shell and thus cause arc-over and puncture. In such cases, the rate of heat withdrawal as by increasing rate of flow of water may be increased, but preferably the electrical energy input to the electrodes i diminished. In this way progressive fusion is achieved at preferably a slow and safe rate, with all factors capable of definite control, including the avoidance of cumulative action like that above mentioned and thus I achieve nicety of control of the point in the 12 progression of fusion downwardly toward the bot tom shell ill at which it is to be halted and cut off. That point may be such that any desired thickness of unfused alumina remain in direct contact with the metal shell, for example, a layer of several inches in thickness.

Also, during the above-described operation, the tilt of the furnace shell it may be varied from time to time or the shell may be rocked slowly back and forth, either from time to time or during the entire operation of pro-forming the bottom and lining; this has the effect of improving symmetry of distribution of the fused portion of the lining and therefore has the effect of shaping the mass of the fused portion of the refractory lining.

If, during the process of forming the bottom, the lump form of alumina was laid in place to terminate in a top surface somewhat as indicated by the broken line 65, the initial and subsequent addition of substantial quantities of powdered alumina during the operation results also in the building up of a lateral or side lining upwardly against the side wall portions l6 and I6, as indicated at M in Figures i and 5, along cross-sectional lines indicated by the full lines 15 in these two figures. In a general way, the volume of material represented by the area included between the broken line 65, the full line 15 and the sides of the furnace shell may be said to represent the additional alumina added at the start and during the continuation of the bottom processing, and the resultant rather substantial concavity thus produced may be said to be the result of a progressive cumulative lateral building up out of alumina particles that are, as to some, fused together and as to others simply sintered together and as to still others, principally those most remote from the region of heat and hence up against the side walls of the furnace shell, a mixture of both types.

This lateral and upwardly tapering buildingup operation proceeds somewhat in the following way: As the initially-added powdered material fuses to start the fusion of the lumps put in the bottom up to the line 65, a puddle of molten or liquid alumina forms in the middle central and more or less circular area just about encompassing the electrode ends as seen in Figure 6; this puddle, which is bounded laterally by the granular or powdered material and is or becomes covered over with more powdered or granular material as the latter is added, increases in Volume and commences to flow or expand radially outwardly on the upper surface E5 of the built-up or lump form of preliminar bottom, and such lateral expansion or movement of the puddle may be aided by the above-mentioned rocking of the furnace.

As it expands radially outwardly, it moves into cooler regions, pushin ahead of it and toward the metal walls of the side shell l6 unfused granular material which thus serves always to protect il'lg not as solid or integral as is the ultimate bottom ingot 14 above described, and is principally a progressivel built-up structure of fused and sintered alumina. particles frozen together because they are thrust radially outwardly into regions of isothermal planes of temperatures too low to maintain them in fused condition and because also they are thrust laterally into the region of cooling effect of the external cooling water upon the side shell [6.

If, however, the bottom lining is initially built up as above described along the broken line 66, tapering it upwardly and outwardly against the sid shell, granular or powdered form of alumina is also added at the start of the bottom-processing operation and may be added from time to time thereafter but in lesser quantity. Again a puddle is initially formed in the central lower portions of the bowl-like face 66 and as the puddle increases in volume, it progresses itself radially outwardly, aided if desired by the rocking of the furnace, and thus molten or fused alumina is in effect washed against and upon the laterally builtup preliminary bottom, enters the interstices, freezes therein and to the lumps and particles, communicates heat to them to facilitate such bonding together or sintering together, and these actions may be accompanied also by some fusion and some sintering together of at least the lumps and particles of the innermost layers or portions of the laterally built-up portions of the structure by heat derived directly from the action of the electrodes. This latter action is analogous to the downward progression of fusion toward the bottom shell IT as above described, but is a radially outward or lateral progression which, however, is less complete due probably to the heat withdrawal by the descending water on the external walls of the side shell.

In either case, that is, whether the start is made along the broken line 65 or the broken line 66, the radial dimensions of the side shell are sufficiently great so that, with respect to the maximum power input needed to process the bottom ingot 61, complete fusion of the upwardly tapered side portions is not effected for otherwise the molten material thereof would seek its own level and thus the lateral lining portions would be destroyed. Thus, while up and down adjustment of the electrodes and accompanying control of Voltage applied and of power input thereto have a major effect in the downward progression of fusion throughout the bottom lining layer, these factors have a lesser effect upon radially outward progression with a given relationship of electrodes to the radius of the side shell, and this is preferred in order to avoid risking complete fusion of the side shell linings and arc-over to and puncturing of the metal side shell itself.

Where adjustment of the three electrodes as to spacings from the side shell is possible or provided, they are adjusted or set to meet the abovedescribed conditions which are satisfactory also, as later described, for the normal functioning of the furnace. A satisfactory relationship, for alumina, may comprise, with electrodes 12" in diameter in Figure 2, spacing them about 42 center to center and giving the distances B in Figure 2 a value on the order of 3 feet where the side shell has a maximum diameter at its base on the order of 11 feet and a minimum diameter (at the top) of about feet.

Due to the shape of the isothermal planes or lines, the final lining, with a concavity somewhat as indicated in the full line in Figures 4 and 5,

is internally defined, by the surface 15 which is substantially a surface of revolution whose generatrix is moved about an axis coincident with the vertical axis P of the furnace structure, and since the front wall l6 is (see Figure 2) straightened out along a chord as above described, the side shell linin is thinner at the flattened front wall I6 as shown at 14 than it is at the arcuate side wall Ni a appears better in Figure 4, for reasons later described. In building up this thinner front wall lining M the alumina freezes onto the internally exposed surfaces of the graphite bushing l8 and in effect bonds itself thereto, and that bushing, as is better shown in Figure 7, and the spout element 46 are of a length to project inwardly beyond the front wall Mi a distance equal to the minimum desired thickness of this thinner front wall lining "M all as is later described.

When the desired depth of fusion in the bottom lining has taken place, the power input to the electrodes is cut down, and the electrodes raised, both at a suitable rate, or the power input is out 01f, so as to commence solidification of the fused alumina from the walls of the furnace shell inwardly at a suitable rate, the water-cooling of shell Ill being continued to prevent undue rise in temperature of the metal shell and also to aid in the solidification, by which there is thus formed a solid ingot or monolith 61 (Figures 4 and 5) of fused but solidified alumina. Its downward and lateral boundary or demarkation is conformed substantially to an upwardly concave isothermal plane and is substantially a portion of a spherical surface spaced from the bottom shell ll by the layer 68, being really a region of transition from the solid ingot '6'! to the layer 63 of partially sintered-together and partially fused lumps and particles. Layer 68 is of the desired and controlled thickness as above described, and provides some degree of play or flexibility between the large integral or unitary lining block or ingot B7 and the metal of the shell to accommodate dimensional changes upon heating and cooling, such as occur during shut-downs or power input changes or changes in rate of heat-abstraction by the external water-cooling.

The solidification inwardly aids in forming the upwardly tapered side portions 14 of the lining and unsolidified alumina may be poured off or may be retained for subsequent furnace operation. The side portions 14 of the lining may comprise as above noted principally partially fused lumps or particles of alumina, fused or sintered together, and they may become added to or further built up during subsequent operation of the furnace as is later described. This portion extends upwardly and about the interior portions of the spout structure (see Figure '7); metal bushing 12 is welded into an opening in the inclined plane wall Hi of the furnace shell l0, preferably with its axis at right angles to the vertical axis of the furnace shell, and the inner end of the metal sleeve 12 projects but very little, if at all, beyond the inner face of the wall Mi The welded junction between it and the wall l6 and the Welded junction thereto of the baffle or shield plate 13 are water-tight so that water running down the outside face of the wall Hi can spread onto and over the metal sleeve 12 to prevent abnormal heatin thereof and of the graphite spout element 40. Within the sleeve 12 is received a graphite bushing 18 which is internally tapered to removably receive the externally tapered spout element 40, and bushing 18 projects inwardly a substantial distance beyond the end it; of the sleeve '12 so as to be engaged and sur-- rounded by and bonded to the lining portion it.

It is about the inwardly projecting portion of the graphite bushing "l8 that the lining material I l extends and becomes bonded or fastened, being in effect solidified thereagainst with sufficient security of fastening as virtually to hold the bushing 18 against removal from the metal sleeve 12. The graphite bushing it thus protects the spout element 40 against having fused alumina frozen against and onto it except for its small end face, and thus permits ease and facility of removal and replacement of the spout element ill itself.

The passageway 79 in the spout element i. preferably tapered and is circular in cross-section; it may be of a length on the order of 12 and it is constructed to function as an orifice to substantially fix or control the rate of flow there-- through of molten or fused material. For that purpose, the inner end 19 of the passageway "It is of appropriate dimensions to function as an orifice and illustratively it may be of a diai'neter of 2". The outer end opening lil of the 19 may be on the order of in diameter. The taper is, accordingly, preferably substantial, to get a better orifice effect and also to provide a progressively increasing channel or passageway that leads away from the orifice it and thus lessen resistance to flow of molten material and hence effect quicker rate of flow, particularly in the case of fused alumina where, according to my invention, it is desirable, where certain characteristics in the ultimate product are desired, toeffect as little loss of heat content during pouring as is possible. Also the spout element l-li is of sub stantial wall thickness, increased by the thickness of the graphite bushing '18, being on the order of 3 or so, thus making for a lesser rate of heat loss therethrough from the high temperature of molten material being passed by the orifice it With a discharge spout construction of the just-described character, I am enabled also to achieve the desired continuity of furnace operation even though, as above mentioned, changes in the structure and thickness of the lining portion 14 (Figures 4 and 6) take place and replace ment of the orifice-spout element ill may be achieved with little or no material interruption in the continuity of the subsequent operation.

It should be noted that, during the processing r of the refractory ingot or monolithic lining to prepare the furnace for subsequent operation, as above described and also during the subsequent operation of the furnace, the top closure or hood structure ll (Figures 1 and 3) is preferably made to coact and to achieve certain unique additional advantages; in this connection, it might at this point be noted that the temperature and heat produced during both lining-formation and subsequent furnace operations are of a high order of magnitude, that during these operations protec tion has to be afforded to the upper portions of the metal side shell 18 which, as indicated in Figures 4 and 5, need not be lined, and that the addition of powdered form of material, such as granulated or finer-grit alumina, during the heavy and substantial and sometimes violent arcing that accompanies the operation of the electrodes presents additional difficulties and hazards. These and other matters and controls I am enabled to take care of in. a thoroughly practical way with the aid of the just-mentioned hood structure.

This hood structure is preferably of a built-up construction and comprises a top plate or roof,

generally indicated by the reference character 81 (see Figure 8) made of suitably heavy sheet steel and having a conformation substantially matching the outline of the upper edge of the side shell it of the furnace shell I0 and it ma be reinforced or strengthened in any suitable Wa as, for example, a peripherally-extending structural steel member 82 of suitable cross-section, such as angle-hon, channel or the like, and by suit-- able transverse structural steel members, preferably of so-called angle section to which the plate 8i may be welded and which in effect form a frame whereby also the plate member 8| need not be in a single piece and hence may be in sections assembled and welded to the various elements of the frame. These transverse members preferably also function for other purposes, preferably in coaction with the electrodes [3, l4 and iii which extend through the roof plate 8| which, for that purpose, is provided with openings or slots 83, 34 and 85, respectively, to permit the electrodes to project therethrough. These slots are wider than the diameter of the electrodes and are of substantial length in the direction of tilt of the furnace structure.

It is preferably with respect to the location of these slots 83, 84 and 85, as indicated in Figure 8, that the transverse frame elements are positioned. Thus two angle-sectioned transverse members ill and 88, facing toward each other, extend parallel to each other and each along one side edge of the slot 83, being welded to the peripheral frame element 82 and to the roof plate ill, and in facing toward each other as better seen in Figure 9, they are thus made to form a pair of ways or guideways for slidably receiving and guiding a metal plate cover 90 which is of materially greater length than the electrode slot or opening 63.

The cover plate 96, in turn, has a round opening 9i therein through which the electrode 13 passes with ample clearance for electrical and mechanical. reasons, and about the round opening 9! is secured a ring 92 which can be formed M up out of angle-sectioned structural steel members and welded to the cover plate 90 to form an inwardly exposed annular seat 93 in which is received and seated a collar 94 made of a suitable non-conductive and semi-refractor material capable of withstanding substantial heat, and a suitable material ma be an asbestos composition, such as asbestos lumber. The collar 94 has an internal diameter materially larger than the diameter of the electrode that passes through it and here a clearance of l or 2 may suffice; its inner face is bevelled at top and bottom so as to avoid presenting for contact with the cylindrical electrode a surface of substantial axial dimension and so as to approximate in a general way a knife edge effect.

The slots 84 and are provided in a similar way with slidable cover plates and insulating collar and since these parts are of similar construction and coact similarly with the electrodes I l and 15, respectively, as do the corresponding parts just described in connection with electrode l3 and slot 83, these parts are similarly numbered in Figure 9 and need not be further described in detail, and the same is true of the pairs of transverse frame angle members 81 and 88 provided for each of the slots for guiding the respective cover plates.

The roof or top structure, such as just described, is made to overlie the upper otherwise open end of the furnace shell ID and it is preferably supported by the latter, but in a position spaced upwardly from the upper edge of the shell by a distance on the order of about 2 feet. Such support may be furnished in any desired or suitable way and, illustratively, by a suitable number of suitably spaced vertical struts 96 which are preferably structural steel elements of any suitable cross-section, illustratively of channel crosssection, and are preferably welded to the roof structure at their upper ends and secured as by welding or preferably by bolting at their lower ends to a structural steel element 91, illustratively of angle section, as is better shown in Figures 10 and 11.

The element 9'! is Welded to the periphery of the side shell it at the inner portion of its hori- Zontal web, the two parts thus giving the upper rim of the metal shell H3 substantial strength and rigidity. Moreover this arrangement, with the vertical web of the member 91 projecting downwardly and spaced from the side shell I6, forms an efficient shield and baffle to prevent water from the uppermost pipe or conduit 69 from splashing or moving over the edge of the shell and into the furnace and, conveniently and preferably, the pipe 59 is substantially housed in the space thus provided, as shown in Figure 11, its bracket support conveniently comprising suitable hookshaped bolts 98 passing through one of the webs as shown. I

Ihe member 91 and shell Ill, mutually reinforcing each other, thus also provide a strong foundation to which to attach the abovedescribed roof structure. In the space between the latter and the upper end of the furnace shell l and between successive vertical struts 96 I mount, preferably removably or movably, side closure members which preferably take the form of doors Hill (Figures 3 and 10) preferably built up and suitably curved or approximately so to substantially conform to the curvature of that particular portion of the upper rim of the furnace shell which they respectively overlie so as to form substantially an upward continuation thereof, and the vertical struts 96 are preferably appropriately spaced to provide, when the doors are open, openings of substantial peripheral extent. Thus, for example, the periphery to be closed by the doors may be divided into six, eight or ten spaces by as many vertical struts 96 to be closed by a corresponding number of doors I00.

As indicated in Figure 10 and also in Figure 3, each strut 96 forms a post to which the hinges lill of one door may be secured and to which one element of any suitable latch structure I02 may be secured for latching the next adjacent door in closed position.

The doors are hung and dimensioned so that they fit relatively snugly along their top edges underneath the roof structure or frame, when in closed position, and leave a substantial space, indicated at IM, between their lower edges and the upper rim of the furnace shell ID, a space on the order of, say, 5". The doors I00 are prefera bly constructed in any suitable way to be resistant to the transmission of heat and thus, referring to Figure 10, each door may comprise a built-up frame I06 of channel cross-section, thus providing two spaced webs I01 and [D8 to which are secured and by which are held in spaced relation wire screen sheets I09 and H0, respectively; the spacing between the latter is substantial and hence the outer screen H0 does not reach the temperature of the inner screen I09.

The doors I05 are large enough to give access into the interior of the furnace for building up the bottom lining as above described and for subsequent maintenance purposes, such as replacement of electrodes. During the operation of the furnace, they are kept closed and their insulation action makes it possible for an operator, standing on an elevated platform (not shown), to work in such close proximity to the furnace, and with comfort and safety, to insert an L-shaped metal probe, earlier above mentioned, through any of the spaces I04 under the doors and hence into the furnace to project it into the bottom undergoing processing or into the subsequent production melt to determine the depth of the fused or molten material; as the probe is withdrawn, fused material freezes to it and by measuring the portion of the probe covered with frozen material, the condition being tested can be determined. Or, if desired, any door may be opened for this probing operation and it is by way of opening a door that the operator may, by a suitable tool, shift or redistribute raw or unfused material being fed to the furnace, should such action be desired. Access in this manner may be gained throughout the entire periphery of the furnace, though in practice these operations can be carried on adequately from one side station of the furnace.

At suitably distributed points, preferably three in number where three electrodes are employed for 3-phase operation and, illustratively, at approximately the mid-points of the sides of the equilateral triangle (Figure 2) formed by the electrodes, I pass through suitable openings in the top plate 8| of the roof structure three preferably flexible conduits, such as flexible metal hose, indicated at H3, H4 and H5 in Figures 1, 2 and 8, providing them with suitable bushings (not shown) of suitable refractory material where they pass through the top plate 3| and thereby also secure them to the latter, but in position to allow suitable lengths of them to depend downwardly within the hood structure, generally parallel to the electrodes and to an extent where they terminate just about in the plane of the top edge of the side shell I6.

At a suitable point above the furnace structure, they are connected to any suitable arrangement or means, preferably controllable or regulatable at will in any suitable way, for substantially equally supplying the feed conduits I l3-l l4l [5 at substantially equal rates with raw or unfused material preferably in granular or powder-like form; such an arrangement and means are diagrammatically indicated in Figure 1 by the reference character H6.

t is by way of these conduits that the addition material, described above during the formation of the bottom lining, is controllably fed to the furnace and these feed conduits function also to supply, preferably continuously at a suitable rate, the material to be treated during the subsequent continuous operation of the furnace, and as later explained, they function to maintain, preferably controllably, a suitable blanket or top layer of unfused material overlying the melt to prevent substantial heat loss or heat flow upwardly from the melt, in effect forming a heatinsulating blanket or layer above the melt. It is this action that contributes toward making it possible to have some of the metal side shell unlined, both during formation of the bottom and side lining and during subsequent furnace operations; the side lining, as earlier noted, need not extend all the way to the top edge of the side 10 shell; this insulating action also contributes toward the feasibility of an all-metal hood struc ture like that above described and to the feasibility of an operator working in close attendance upon and to the furnace.

But the supply of powdered or even granular material in this manner can give rise to dust production, aggravated by the fineness of the particle form in which the material is supplied, largely because of the substantial agitation of the material of the above-mentioned layer or blanket in the regions close to and around the electrodes, because of the agitation thereof caused by the arcs. Accordingly, I connect, at a suitable point or points, preferably as near the middle point as possible, in the top plate 8| (see Figure 8) a relatively large flexible conduit N8, of any suitable and preferably flexible material, such as flexible hose, providing the roof plate 18 with a suitable opening and with suitable means for securing the conduit H8 thereto. The conduit extends upwardly where it is connected to a suitable suction and separator means of any suitable construction and hence only diagrammatically indicated at H9 in Figure 1. The device I I9, including some such means as a suction fan, thus draws air out of the hood structure at a suitable rate to carry with it particles of the in-fed material and of the above-mentioned blanket that are agitated or projected into sus-- pension in the air, and in this connection the screen construction of the doors I (Figure and the provision of the spaces I04 beneath them and also the spaces between the electrodes and the collars 94 (Figure 9) provide for adequate ingress of fresh air from the outside atmosphere, such ingress preventing egress of dust. The resultant movement of air takes with it suspended particles or dust and also some heat, thus contributing toward prevention of undue temperature rise in and within the hood structure itself.

During tilt of the furnace structure l0 during either bottom-lining formation or subsequent furnace operations, the hood structure ll tilts with the furnace structure as a part thereof, but closure of the electrode slots 83, 84 and 85 (Figures 8 and 9) is maintained by their cover plates 90 which are held against movement by the nontilting electrodes, the resultant relative movement being a sliding movement between the cover plates 90 and their respective guideways 81-88. During tilting movement, the lcoseness of fit between the insulating rings 94 and the electrodes, aided by the shape of the inner faces of the collars 94, avoids binding between the electrodes and the collars and insures nicety of the just-mentioned relative sliding movement of the other parts. The flexibility of the infeecl conduits and of the dust-collecting conduit maintains continuity of their operation and action during tilting.

With the bottom and side lining formed as above described and the furnace otherwise ready for operation, a charge of granular or powdered material is fed to the furnace and on top of the integral or monolithic lining, the electrodes are let down, starting graphite bars or rods are inserted and the electrical energy turned on, whence arcing commences followed by progressive fusion of the mass of the charge, the starting graphite rods being preferably removed after starting is completed. Progressively, and by continuing the feed of material through the infeed conduits ll3- IM-I I5, a melt or molten mass is built up or produced to a substantial depth above the bottom-lining monolith or ingot 67, for example, a depth on the order of about the height of the orifice-spout element whose vertical position, as shown in Figure 4, is related to certain of the thermal conditions brought controllably into existence during the operation of the furnace and to the approximate capacity at which the process and apparatus are to operate. With a furnace shell l0 structurally dimensioned on the order of those dimensions above mentioned and with the side shell it having a vertical dimension of about 6 feet, and for a capacity on the order of 5,000 or 6,000 pounds of fused alumina per hour, the orifice-spout 40 is positioned about 2 feet down from the upper edge of the side shell; with a maximum thickness of 30" of pro-formed bottom lining (the solid mass 61 in Figures 4. and 5), this would mean that the melt is produced or built up as above described to a quantity of about 12,000 pounds or about 6 tons, whence tilting of the furnace out of normal vertical position and for pouring through the orifice-spout ill may be commenced.

Of this molten mass, only a portion is drawn off during the tilting and where the melt is on the order of 12,000 pounds, the portion drawn off, in a detailed manner later explained, is only about one-third, namely, about 4,000 pounds. This is set forth as illustrative and the portion drawn off may be varied throughout some range, having due regard for the controls that I effect during the production of the melt and during subsequent building up of another melt in which the deficiency caused by the portion drawn off, is made up.

Bearing in mind that, in the case of alumina, the melting point i exceedingly high and that reliance is placed upon the same material, namely, fused alumina for preventing any of the melt or any fusion from proceeding to the metal shell itself, the factors of energy input to the elec trodes, the voltage applied thereto, and the ver tical elevation thereof are, and can be, I have discovered, so controlled and interrelated, checked by probing as earlier above described, as will maintain the bottom-lining ingot 07 (illustratively 3 thick) with its integral built-up side lining portion or extension 14, intact and uninvaded by any, or any material, fusion, throughout long-continued operation over a period of months, thus avoiding damage to the metal shell of the furnace. According to my invention, it is possible to maintain the dimension of the lining structure, particularly the thickness of the bottom-lining ingot 67, within a close limits as may be desired, against various variables, including such factors a change in conductivity of the material undergoing treatment, the efliciency of melting or fusion, or even change in temperature of cooling water initially supplied to the external surfaces of the furnace shell ID, or if desired, the lining thickness may be increased, or even de creased under control, though to decrease it in thickness would be to lessen the factor of safety initially decided upon. In effect, I effect control of the electrical factors in such a way as to insure that the curved and upwardly convex plane or surface 15 (Figures 4 and 5) coincides, or substantially so, with that isothermal plane or surface that is of a temperature, in relation to other and generally geometrically similar isothermal planes or lines in the body of the melt itself, just below the fusion point of the material in question, such as alumina. If that isothermal plane or line is not permitted to progress down- 21 wardly below that indicated by the line 15 in Figures 4 and 5, melting or fusion of the lining does not take place and its dimension is retained; if conditions change so that that isothermal plane or line moves upwardly, the thickness of the lining is added to.

The molten material is conductive and its resistance to current flow from one electrode to another is one factor, while the contact resistances, each usually in the form of an arc, between the molten material and each electrode of any pair of electrodes represent two additional factors, the three resistance factors being in series in the path from one electrode to its coacting electrode. I have discovered that the shape and curvature of the isothermal planes or lines is variable in accordance with the relationship between these resistance factors. For example, it i possible to have such a relationship between them that, looking at Figures 4 and 6, the bottom ingot 61 can be built up in thickness in a somewhat conical form coaxial with the axis P or, conversely, can be thinned down in a somewhat annular depression underlying a circle drawn through the centers of the three electrodes, leaving an upstanding somewhat conical central projection coaxial with the axis P.

The relative values of these factors can be changed by raising or lowering the electrodes, thereby altering the contact or are resistance factors, and with constant current flowing in the circuit of any pair of electrodes and hence through the three series resistances, the heating efiects produced by any two electrodes in the respective regions where the three resistance factors are present may be varied. For example, the measure of the heat effect is 1 R, and for a given power input, that portion of it that appears a heat energy in the resistance factor of the molten material itself can be increased or decreased as the contact or are resistance factors are decreased or increased, respectively.

Accordingly, should the isothermal plane or line I (Figures 4 and 5) start moving downwardly so as to cause fusion to invade the bottom-lining ingot or monolith 61, and. this action is detectible by periodic probing as above described, corrective action is taken and this may be achieved in various ways. For example, the electrodes may be moved upwardly, thus to increase the arcresistances and, assuming a fixed applied voltage, the current and hence power input diminishes correspondingly, the total or overall production of heat diminishing inversely as the square of the current and directly as the increase in resistance. Increase in the arc resistances, in relation to the resistance of the molten material itself, effects, it will be seen, a redistribution of heat energy in that a lesser amount is directly produced in the molten material itself, and a greater amount is produced in the upper or surface portions thereof and thus also more heat energy is directed to the unfused material that forms the abovementioned blanket and which i continuously being supplied through the infeed conduits I I3 |l4-ll5. Stated differently, these actions halt the downward progression of the isothermal plane or line 15. A broadly similar halting of downward progression may be effected by cutting down on the current and hence power input by any suitable means as, for example, by cutting down on the applied voltage, leaving the electrodes more or less in the same position. Should the probing indicate that the curved isothermal plane or line 15 i moving upwardly, so as to increase the thickness of the bottom-lining ingot or monolith 61, reverse corrective steps are taken, as will now be clear.

However, for achieving better efliciency and also continuity of rate of operation, I prefer to employ corrective controls that avoid substantial fluctuations in power input, with accompanying necessary changes in infeed of unfused material, as would be the case if the above-described corrective controls are employed, thus also achieving the advantages of substantial continuity of electrical load or demand. Such preferred controls can be effected manually, but preferably are effected automatically; in a preferred mode of operation, I maintain substantial constancy of current input at selected standards, for any one of which the positions of the electrodes are varied to achieve current constancy, and the applied voltage may be different for each standard of current constancy. To the resultant substantial constancy (for any selected standard of current constancy) of heat energy produced in the furnace I am enabled to correlate thereto a corresponding steady or continuou rate of infeed of unfused material through the infeed conduits and also maintain the resultant progressively increasing mass of the melt in proper molten condition for periodic but continuous pouring of a portion thereof through the orifice-spout 40, while at the same time maintaining integrity of both the bottom-lining ingot 61 with its integral side lining extension 14.

In this preferred method, referring now to the diagrammatic showing in Figure 12, the electrodes are connected to a suitable source of alternating current energy and in the case of a 3-electrode furnace, the source is polyphase and is preferably 3-phase, the B-phase energy being supplied from a suitable source, preferably through step-down transformers provided with suitable means whereby the output voltage applied to the electrodes l3, l4 and I5 may be varied. Thus, I may employ three transformers T T and T whose high-voltage windings H 1-1 and H may be connected in any suitable polyphase arrangement, such as the delta connection as shown, to the polyphase source by suitable conductors ll5--l !6I 11; preferably I provide also any suitable switching and automatic cut-out means for controlling the main power circuit and for cut-out upon overload, and such a means I have shown diagrammatically at I [9.

The low voltage winding L L and L3 may also be given any desired polyphase connection such as the delta connection shown, and connected by conductors I22, I23, and I24 to the three electrodes as indicated in Figure 12.

The control apparatus 32 includes, as above mentioned, a suitable means for raising and lowering the electrode masts I9, 20 and 2|, individually, each preferably motor-operated and relaycontrolled in any suitable or known manner; they are diagrammatically indicated at l25 I25 and [25 and collectively by the reference character I25 in Figure 12. Each electrode control I arrange for manual control, and preferably also to be automatically controlled or actuated, preferably in response to current flowing tothe electrodes and hence, conveniently, in response to current flow in the respective phases. Such automatic controls can be substantially identical for each electrode mast, and hence it will suffice to describe in detail only one of them, the corresponding elements of the others being indicated by the same reference characters distinguished by correspondingly different exponents; thus, for the phase leading to electrode I may provide a current-responsive coil or winding tit con-- nected by conductors lt'i irfii to a device lilil which may be a suitable low resistance but is preferably a current transformer having its pri mary connected in the low voltage conductor IN leading to the electrodes and having its secondary connected to the winding H25 so that changes in current flow in conductor iii are reflected in the winding i225 which, through suitable means such an armature adjustably biased by an adjustable spring iii-l may be made to close a circuit at contact ltd upon increase in current above the desired value and close a circuit at contact iliil upon decrease in current from the desired value. These contacts are connected by conductors lfili and iii to the raising and lowering mechanism i25 for electrode iii, being connected in circuit with a suitable source i354 of operating voltage, by conductors i lil and Idl In like manner, monitor windings i126" and I726 respond to current changes in conductors I23 and IE2, respectively, by way of the transformers i239 and i36 connected in the circuit of these conductors, for controlling the raising and lowering mechanisms iilfi and i235 for the electrodes 14 and i3, respectively. So long as the desired current value exists in each phase, the armatures of the monitor windings can assume and retain a neutral position, that is, a position intermediate or their respective contacts, and mechanisms mil i125 and 25 hold their respective electrodes at rest.

The mechanisms Nit iiiii and ifit' however, move their respective electrodes upwardly when their respective control or relay circuits are closed at contacts Hi l w t and i34 and move them downwardly when closed at contacts new, i35 and WW, in each case to restore the current val ues in the three phases to the desired value.

Each of the mechanism i225, lifi and M5 may comprise, as above indicated, a winch operated by a reversible motor which is preferably a direct current motor in which case the justmentioned contacts operate suitable relays in such manner that the polarity of current supplied the motor armature is in one direction when the circuits are closed at contacts lad iii l and 134 thus to cause motor rotation in a direction to raise the electrodes, while the polarity is in reverse direction when the circuits are closed at contacts llfi iSii and i325 and the motor drive is thus also in reverse direction so as to lower the electrodes. Preferably, suitable manual controls H9 5 i29 and i29 are provided, collectively indi cated in Figure 12 by the reference character I29 and respectively connected in parallel, as diagrammatically indicated, with the just-described contacts and associated armatures so that the electrodeu'aising and lowering mechanism may be manually controlled if desired, and any suitable circuit arrangements or switches may be employed to shift the control of the electrode mechanisms Hi5 from the manual control i223 to the monitor winding control or vice versa.

During operation of the furnace, the latter being a resistance and hence a substantially non inductive load, the current and hence energy in put to the furnace may be maintained constant under the control of the regulating apparatus which is monitored by the current-responsive windings tild H6 and iilil Should the current value increase, the corresponding mechanism raises its electrode to increase the contact or are resistance factors to a point to restore the current to the desired value whereas a drop in the current flow to the furnace causes lowering of the electrode to diminish the contact or are resistance factors to a point to restore current flow to the intended value. With a furnace or size and capacity like that above mentioned, the currentresponsive controls may be set to maintain sub stantial constancy of power input at a figure on the order of 4,000 kilowatts, at a voltage on the order or 220 volts, the voltage, of course, varying somewhat as will be understood as a result of the regulating action caused by the constant current monitors iiili E26 and [25 but on the whole remaining, or being held, substantially constant for a given standard of current constancy as set by the control lid, lilil and i20 For convenience, the monitor windings i28 I26 and H6 are hereafter referred to as the monttor winding i526, and the three windings are diagrammatically indicated at H26 in Figure 12 as making up a single unit.

Under these conditions of constant power input thus automatically achieved, the condition of the bottom-lining monolith or ingot B7 is periodically explored by the probe as above described and if it is found that fusion thereof is taking place and that hence the above-mentioned isothermal plane or line "i5 is moving downwardly, so as to diminish the thickness of the solid and unfused protective bottom lining, the manual control I20 is to a somewhat lower value or standard of current constancy to be maintained, thus increasing somewhat the voltage of the output of the low voltage windings or" the transformers but on the whole decreasing the power input to the furnace electrodes, the power input being a function of the square of the current. Such resetting of the three controls lzfl IZG and 12!] (collectively referred to by the reference 12(l) is in a direction to increase their respective resistances, causing more of the output of the respective current transformers thereafter to flow through the monitor windings IZG and iiiti than did prior to the adjustment. That manual operation of resetting the standard of operation of the constant current monitor windil'lg I26 (by setting the control l2tl) causes the electrode mechanisms M5, I25 and I25 to raise their respective electrodes to increase the are resistance relative to the resistance of the melt, cutting the current down to the new standard, and thereafter to maintain constancy of current and power input, but now at a higher standard of electrode elevation and a higher standard of voltage constancy than theretofore. The downward progression of the critical isothermal plane or line is halted, and if the resetting has been made in sufficient magnitude, that plane or line may be made to recede upwardly and thus to restore the thickness of the solidified bottom-lining or even to increase it if desired, as will now be clear,

If the probing indicates that the bottom-dining being increased in thickness, that is, that the isothermal plane or line i5 is moving upwardly beyond the optimum or desired bottom-lining thickness, the manual controls I26 i20 and c are set in reverse direction, resulting in a reverse operation in that the now lower current flow in windings i26 M6 and H25 gives them a diiferem standard of operation, bringing the monitor windings into action, by closing the control circuits at contacts I 35' and l35, to

lower the electrodes to a point where the now higher standard of current value and power input are achieved and thereafter maintained, the electrodes now operating at a new but lower standard of elevation than theretofore.

Thus, during operation, the integrity and safety of the bottom-lining ingot 61 may be dependably maintained, and therewith also the in tegrity and safety of the side lining 14, With constancy of power input during operation, also, substantial variation in radial thickness, as viewed in Figure 6, of the side lining l4 and 14 is avoided, for material decreas in power input, without more, would have the practical effect of warping or drawing the side of vertical portions of the isothermal lining 14 (Figures 4 and 5) inwardly toward the electrodes, thus building up the lining to greater thickness than is necessary by permitting solidification thereagainst, and hence growth in radial thickness, of alumina, while too great a power input, without attention to other factors, would have in general a reverse effect, bringing about a thinning down of the lateral lining portions, though in all of these connections, other factors are interrelated as later explained.

It is preferably with such controls, either manual or automatic or both, that the earlier abovedescribed formation of the bottom and side lining is effected, as will now be clear, and for any desired period or periods during the formation of the bottom and side linings, the current, voltage,

and power input may be automatically maintained constant for such successive intervals of time and at such successiv values as are dictated by the progression of fusion as earlier above described.

Operating the furnaces at values on the order of magnitude of those above mentioned, there are constantly brought into coaction other factors, principally the preferably continuous and steady infeed of unfused alumina through the infeed conduits ll3-I l4l 15 at a rat on the order of 6,500 pounds per hour; at this rate the unfused material is steadily distributed on top of the existing melt, and if necessary, the operator may, by means of a suitable tool inserted through the peripheral openings I04 (Figure underneath the doors I00, flex or move the inwardly depending portions of these flexible infeed conduits so as to bring more material to different regions as may be desired or as may be indicated by the probing operations. The power input, at constant rate, on the order of 4,000 kilowatts, thus goes to maintain molten the existing melt as against heat losses and particularly as against the protective heat-withdrawing action of the water being run against the externa1 surface of the furnace l0 and to supply th heat energy to convert the in-fed material to molten condition at substantially the rate of its infeed, while maintaining the above-mentioned blanket-like layer of several inches thickness always on the top of the melt to oppose heat loss, from the power input and the melt, to the highly heatconductive un-lined upper wall portions of the side shell l6, thus contributing to the protection of the latter, and to oppose heat loss upwardly into the hood.

When the total melt, under the just-described actions, reaches about 12,000 pounds in quantity, and this may be determined or known from the feed and distribution mechanism H6 (Figure 1) which includes any suitable measuring or continuous weighing mechanism, the upper level of the melt is at or above the orifice-spout 40, and pouring may now be commenced at a suitable rate and in so doing it is not necessary to interrupt the continued feed of unfused material to the furnace or the power input to the electrodes; the furnace is tilted as above described, in clockwise direction as viewed in Figure 1, to bring the orifice l9 at the inner end of the orifice-spout 40 well below the upper level of the molten or liquid alumina and hence also well below the relatively thick blanket of unfused alumina which overlies, or floats upon, the just-mentioned level or upper surface of the liquid material and thereby risk of contaminating the molten material that flows out of the orifice-spout with unfused or partially fused material is minimized. The electrodes do not tilt and thus maintain, during the actual tilting and after tilting is completed, substantially the same relationship to the melt and the blanket and to continuing inflow from above of unfused material as they did theretofore, the top surface of the melt remaining level or horizontal and the general relationship of having the lower ends of th electrodes terminate in substantially a horizontal plane and hence in a plane parallel to the surface of the furnace contents remaining unchanged.

The electrodes may thus continue to operate as before, the power input continuing under the control of th monitor winding I25, and the water-cooling flow being likewise continued, the upward and inward slope of the front wall [6 being sufficiently great so that, even during maximum tilt (about 10) the cooling water continues to run down along it and not off of it before it reaches the lower end of the front wall, and the infeed of unfused or raw material likewise continues preferably at the same rate as before. The front wall l6 and adjacent portions of the side wall l6 are protected by the lining portion I l which has been built up as above described, preferably with the aid of rocking or tilting of the furnace NJ as was earlier above pointed out; in fact, as above pointed out, the side lining portions i l and (4 may be, during the normal operation of the furnace, built up in both radial and vertical directions by the freezing thereagainst of partially fused or fused material, probably intermingled with unfused material from the blanket layer itself, as the level within the furnace rises during the continued infeed of material and fusion, prior to tilt of the furnace.

The extent of tilt is relatively small and thus the relationship between the non-tilting electrodes and the bottom-lining structure which tilts with the furnace, is not greatly disturbed, but since the period of pouring is relativel short, being on the order of ten minutes, disturbance of this relationship during the period of pouring is not great and can be corrected and compensated for upon the return tilt to normal of the furnace structure.

With the above indicated order of magnitude of values, the orifice 19 has a preferred capacity of about 500 pounds of molten alumina per minute, determined preferably empirically, and with the dimensions of the spout element 40 as above set forth, the orifice 19*, having a diameter of 2", gives a controlled rate of flow on the order of 500 pounds of molten alumina per minute, under the conditions of hydraulic head met with during tilt. In this connection, as the level of the liquid alumina is drawn down by the pour, the tilt of the furnace may be progressively increased if desired to further lower the orifice element and thus 

